Field
Embodiments described generally relate to methods and systems for producing urea.
Description of the Related Art
Urea can be synthesized by a two reaction process that initially includes reacting ammonia and carbon dioxide to form ammonium carbamate, and subsequently, decomposing the ammonium carbamate to form urea and water. The reaction of ammonia and carbon dioxide to form urea can be described using the following equilibrium reactions:2NH3+CO2NH2COONH4  (ammonium carbamate, exothermic)NH2COONH4H2O+NH2CONH2  (water and urea, endothermic)
The first reaction for producing ammonium carbamate is an exothermic reaction and essentially goes to completion. The second reaction for producing urea and water is endothermic and usually does not go to completion. The conversion of ammonium carbamate to urea decreases as the concentration of water or the H2O/CO2 ratio in the reaction mixture increases. In addition, the conversion of ammonium carbamate to urea increases as the temperature or the NH3/CO2 ratio increases. The resulting urea solution contains one or more contaminants, including water, ammonia, carbon dioxide, and ammonium carbamate, which must be removed to produce a purified urea product.
There is a need therefore, for improved methods and systems for making urea at increased yields and/or increased purity relative to conventional methods.